1. Field of the Invention
The present invention relates to an air filter part having a filter medium capable of cleaning air in at least a portion thereof, and a method of packaging the air filter part. The air filter part is contained in a package that suppresses the absorption of organic substances by the air filter part and a method of packaging the air filter part.
2. Background Information
In a clean room or in a semiconductor production device, electronic parts such as semiconductors, liquid display devices are produced in an environment in which the air is treated to capture floating particles. For example, an air filter unit having high collection efficiency, such as HEPA (high efficiency particulate air) filter or ULPA (ultra low penetration air) filter is used to capture floating finer particles in a clean room or in a semiconductor production device. The air filter unit of this type is typically a unit equipped with a high collection type filter medium and a frame having the filter medium incorporated therein. The filter medium is formed by, for example, laminating a porous film formed by laminating polytetrafluoroethylene (hereinafter referred to as xe2x80x9cPTFExe2x80x9d for simplicity) and non-woven fabrics arranged so as to interpose the PTFE porous film from both sides thereof. The filter medium is processed in a given shape that is incorporated inside the frame.
When such an air filter unit is placed at an airway of a clean room and operation is started, air outside the clean room permeates the air filter unit and is introduced into the clean room from the airway. At that time, floating fine particles in air are captured by the filter medium by the colliding fibers of the filter medium.
The air filter unit of this type is generally packed in a bag made of a resin such as polyethylene (hereinafter referred to as xe2x80x9cPExe2x80x9d for simplicity) after production, the bag is further packaged with cardboard, and the package is then delivered. Furthermore, there is the case that a filter medium and a product obtained by processing the filter medium into a given shape (hereinafter referred to as an xe2x80x9cair filter pleat packxe2x80x9d) are each independently delivered in the state that it is packaged with the PE bag, the cardboard or the like.
Not only floating fine particles but also gaseous organic substances generated from paint or the like on walls of a clean room although a slight amount floats in a clean room. If those substances adhere onto semiconductor elements, wafers or the like, the electric properties of the products are impaired, and this results in decrease in the quality of products. In particular, high boiling point substances such as dioctyl phthalate (hereinafter referred to as xe2x80x9cDOPxe2x80x9d for simplicity), dibutyl phthalate (hereinafter referred to as xe2x80x9cDBPxe2x80x9d for simplicity), hydrocarbons having at least 15 carbon atoms or the like are difficult to volatilize. As a result, once those substances are adhered onto products, it is difficult to remove those substances from the products. For this reason, a chemical filter is often arranged within the clean room in order to remove those organic substances, and the amount of floating substances is suppressed to a predetermined standard or less.
However, according to the recent studies by the applicant of the present invention, it has been understood that those organic substances are generated not only from the interior walls of the clean room, but also from the air filter unit itself arranged within the clean room. In addition, it has been determined that those organic substances are generated from outside air and in particular from cardboard as a packaging material, and adsorbed on the filter medium, and the organic substances may possibly be generated from the PE bag.
In the conventional packaging form, a filter material such as a PE bag is arranged between an air filter unit and cardboard. Since organic substances generated from the cardboard permeate the PE bag, the organic substances are already in a state of adhering to the filter medium before use. Similar problems like this also occur in the case where a filter medium or the air filter pleat pack is independently packaged. In particular, a high collection type filter medium using PTFE porous film is more apt to adsorb such organic substances as compared with the conventional glass filter medium.
An air filter unit disclosed in Japanese Patent Laid-Open Application No. Hei 10-286415 is already proposed as an air filter part, in which content of organic substances is suppressed to a predetermined amount or less. In the air filter unit disclosed in this Japanese publication, measurement of the content of organic substances is conducted by a purge and trap method. In this conventional method, air having a temperature of about 40xc2x0 C. is blown through an air filter unit at a predetermined flow rate. Then, the amount of organic substances detected from the air permeating through the other side of the air filter unit is measured. Thus, the amount of organic substances contained in the air filter unit is measured.
In this method, organic substances having relatively low boiling point can effectively be measured. However, regarding organic substances having high boiling point such as boiling point exceeding 270xc2x0 C., since measurement conditions are mild, the organic substances cannot sufficiently be separated from the air filter unit. As a result, the content of high boiling point substances such as DBP or DOP cannot effectively be measured.
In view of the above, there exists a need for an air filter part which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
Accordingly, an object of the present invention is to suppress adhesion of organic substances from the packaging onto an air filter.
The present invention provides an air filter part having a filter medium capable of cleaning air in at least a portion thereof, in which the DBP content per 1 g of the filter medium is 1.0 xcexcg or less prior to use of the filter medium.
The xe2x80x9cair filter partxe2x80x9d of the present invention as used herein includes, for example, but not limited to, a filter medium, an air filter pleat pack and an air filter unit (each being described hereinafter). The air filter unit is mainly explained below as an example of the air filter part.
As previously mentioned, although in slight amounts, gaseous organic substances such as DBP, DOP, hydrocarbons having at least 15 carbon atoms, and the like are generated from paint or the like on the interior walls of the clean room. These gaseous organic substances can degrade the products being produced in the clean room. For example, a chemical filter is typically arranged in the clean room in order to remove the organic substances. Thus, the amount of floating substances in the clean room is suppressed to a predetermined standard or less.
However, according to the recent studies by the applicant of the present invention, it has been understood that those organic substances are generated not only from the interior walls of the clean room, but also from the air filter unit itself arranged in the clean room or a semiconductor production device or the like. In addition, it has been determined from the studies by the applicant of the present invention that the air filter unit is already in a state contaminated with those organic substances prior to using the same.
Therefore, the air filter part of the present invention is prepared such that the DBP content per 1 g of a filter medium is a given predetermined amount or less prior to use, and thus, the inside of the clean room is suppressed from contamination in the case where the air filter part is arranged in the clean room.
The term xe2x80x9cprior to usexe2x80x9d as used herein means the time at which the package of the air filter unit is opened after at least about 50 hours in the package so as to remove the air filter part containing the filter medium. The DBP content per 1 g of the filter medium is preferably 0.2 xcexcm/g or less prior to use of the filter medium.
It is desirable in the air filter part of the present invention to measure the content of high boiling point substances such as DBP or DOP by a measurement method such as a hexane extraction method (described hereinafter) that can separate a sufficient amount of organic substances having high boiling point as compared with the purge and trap method.
According to a second aspect of the present invention, the DOP content in the air filter part of a first aspect of the present invention is 1.0 xcexcg or less per 1 g of a filter medium prior to use of the filter medium. In this air filter part, the DOP content per 1 g of a filter medium is less than a predetermined amount prior to use. Due to this, in the case where the air filter part prior to use is arranged in a clean room, the inside of the clean room can be suppressed from contamination. The DOP content per 1 g of the filter medium is preferably 0.2 xcexcg/g or less prior to use of the filter medium.
According to a third aspect of the present invention, the air filter part of the first or second aspect of the present invention, the content of hydrocarbons having at least 15 or more carbon atoms per 1 g of the filter medium is 50 xcexcg or less prior to use of the filter medium. In this air filter part, the content of hydrocarbons having at least 15 carbon atoms per 1 g of a filter medium is less than a predetermined amount prior to use of the filter medium. Due to this, in the case where the air filter part prior to use is arranged in a clean room, the inside of a clean room can be suppressed from contamination. The content of hydrocarbons having at least 15 carbon atoms per 1 g of a filter medium is preferably 20 xcexcg/g or less.
According to a fourth aspect of the present invention, the air filter part of any one of the first to third aspects of the present invention, the filter medium comprises a filter layer at least partially constructed of a PTFE porous film and an air-permeable support material laminated on at least one side of the filter layer. A conventional filter medium for an air filter, such as a glass filter medium, is made of fibers which have large diameters and has large space between fibers. For this reason, the glass filter medium has relatively small adsorption of gaseous organic substances such as DBP or DOP.
On the other hand, in the high collection type filter medium using a PTFE porous film, the fibers are fine with the space between the fibers being relatively small as compared with the conventional glass filter medium.
However, since the high collection type filter medium using a PTFE porous film has a fine fiber diameter, it is more likely liable to adsorb gaseous organic substances such as DBP or DOP as compared with the conventional glass filter medium. Therefore, in the air filter part, particularly the air filter part using a PTFE porous film, the content of organic substances such as DBP or DOP per 1 g of the filter medium prior to use is determined to be less than the predetermined amount. Due to this, even in the case where the air filter part using the PTFE porous film is arranged in a clean room, the clean room can effectively be suppressed from contamination.
According to a fifth aspect of the present invention, in the air filter part of any one of the first to fourth aspects of the present invention, the filter medium has a PF (Performance Factor) value of 20 or more. The collection efficiency and the pressure loss are two characteristics used to determine the performance of a filter medium. The PF value is calculated by the following equation:
PF=[xe2x88x92log(penetration(%)/100)/(pressure loss (pa)/9.8]xc3x97100 in which penetration(%)=100xe2x88x92collection efficiency(%).
The pressure loss in this equation is determined by passing air through the filter medium at a flow velocity of 53 mm/sec and measuring the pressure differential between the air pressure on both sides of the filter. The collection efficiency in this equation is determined by measuring the amount of DOP having a particle size in the range of 0.10 xcexcm to 0.12 xcexcm that passes through the filter medium.
The PF (Performance Factor) value is frequently used as a measure for observing balance of the collection efficiency and the pressure loss. It is considered that a filter medium having a high collection efficiency and a small pressure loss increases the PF value of the filter medium.
The high collection type filter medium using a PTFE porous film is liable to adsorb organic substances such as DBP or DOP as previously described, and a filter medium having a high PF value has particularly strong tendency to adsorb such organic substances.
The air filter part, particularly the air filter part having a PF value higher than a predetermined value, is manufactured such that the content of organic substances such as DBP or DOP is less than the predetermined amount. For this reason, even in the case where the air filter part having a high PF value is arranged in a clean room, the clean room can effectively be suppressed from contamination.
As the PF of the air filter part increases, the structure of the air filter part more readily adsorbs organic substances such as DBP or DOP. The reason for this is as follows. The fiber diameter of a PTFE porous film used as an air filter is generally small as about 0.05 xcexcm to 0.2 xcexcm. As the PF value increases, the fiber diameter becomes finer. If the PF value exceeds 22, the fiber diameter will be 0.14 xcexcm or less, further about 0.05 xcexcm to 0.1 xcexcm. Therefore, the PF value of the air filter part of the present invention preferably exceeds 22.
Thus, according to a sixth aspect of the present invention, in the air filter part of the fifth aspect of the present invention, the filter medium has a PF value exceeding 22.
A package of the air filter part according to a seventh aspect of the present invention comprises the air filter part of any one of the first to sixth aspects of the present invention and a packaging material arranged so as to shield the air filter part from outside air. The air filter part, such as an air filter unit, is packed in a bag made of a resin such as PE after production thereof. The air filter part packed in a bag is further packaged with cardboard or the like. The package is then delivered, as described above. It has been considered that by shielding the air filter part from outside air until use, the air filter part can maintain a clean state as when produced in a factory.
However, it has been determined as described above that the air filter part using a PTFE porous film, particularly one with high PF value, is already contaminated with organic substances such as DBP or DOP prior to use. Furthermore, it has become apparent from the studies by the applicant of the present invention that those organic substances are generated from outside air and packaging material such as cardboard. Thus, those organic substances are possibly adsorbed on the air filter part by permeating the PE bag. Furthermore, it has become apparent from the studies by the applicant of the present invention that those organic substances may be possibly generated from the PE bag itself.
In the package of the air filter part of the present invention, the air filter part is packaged so as to be shielded from outside air by the packaging material, and the air filter unit is packaged such that the content of organic substances such as DBP or DOP is below the predetermined amount even if the package is opened after the passage of a certain time from packaging.
Therefore, adhesion of organic substances such as DBP or DOP to the air filter part in the packaged state is suppressed in this embodiment.
According to an eighth aspect of the present invention, the packaging material for the package of the air filter part has a first material with a polyester film layer in at least a portion thereof. In the package of the air filter part, the first material contained in the packaging material has a polyester film layer capable of shielding permeation of organic substances such as DBP or DOP. As a result, the organic substances in the outside air scarcely permeate through the first material to enter inside the first material. Therefore, adhesion of organic substances such as DBP or DOP to the air filter part in the packaged state is suppressed in this embodiment. The polyester film layer is preferably a film layer constructed of polyethylene terephthalate (hereinafter referred to as xe2x80x9cPETxe2x80x9d for simplicity).
According to a ninth aspect of the present invention, the package of the air filter part comprises the air filter part having a filter medium in at least a portion thereof capable of cleaning air, and a packaging material arranged so as to shield the air filter part from outside air. The packaging material has a first material having an oxygen permeability of less than 20,000 ml/(m2xc2x7dayxc2x7Mpa). As mentioned above, it has been considered that the air filter part can maintain a clean state as when produced in a factory by being shielded from outside air by the packaging material until use. However, it has become apparent by the studies of the applicant of the present invention that those organic substances generated from the outside air and the cardboard of the packaging material permeate a PE bag and are absorbed into the filter medium. Moreover, those organic substances may also be possibly generated from the PE bag itself. Therefore, in the package of the air filter part, the air filter part is packaged with the first material having oxygen permeability lower than the predetermined value. Thus, gaseous substances in outside air are suppressed from permeating the first material. Therefore, adhesion of organic substances to the air filter part in the packaged state is suppressed in this embodiment.
The first material of the packaging has an oxygen permeability of preferably less than approximately 10,000 ml/(m2xc2x7dayxc2x7Mpa), more preferably between 0 and 5,000 ml/(m2xc2x7dayxc2x7Mpa), and most preferably between 0 and 2,700 ml/(m2xc2x7dayxc2x7Mpa). The oxygen permeability is a value measured according to a measurement method defined by JIS-Z-1707.
According to a tenth aspect of the present invention, in the package of the air filter part of the ninth aspect of the present invention, the filter medium comprises a filter layer at least partially constructed of a PTFE porous film and an air-permeable support material laminated on at least one side of the filter layer. The filter medium preferably has air-permeable support layers laminated on both sides of the filter layer by heat fusing.
According to an eleventh aspect of the present invention, in the package of the air filter part of the ninth or tenth aspect of the present invention, the filter medium has a PF value of 20 or more. The PF value is calculated by the following equation:
PF=[xe2x88x92log(penetration(%)/100)/(pressure loss(pa)/9.8]xc3x97100 in which penetration(%)=100xe2x88x92collection efficiency(%).
The pressure loss in this equation is determined by passing air through the filter medium at a flow velocity of 53 mm/sec and measuring the pressure differential between the air pressure on both sides of the filter. The collection efficiency in this equation is determined by measuring the amount of DOP having a particle size in the range of 0.10 xcexcm to 0.12 xcexcm that passes through the filter medium.
According to a twelfth aspect of the present invention, in the package of the air filter part of the eleventh aspect of the present invention, the filter medium has PF value exceeding 22.
According to a thirteenth aspect of the present invention, in the package of the air filter part of any one of the ninth to twelfth aspects of the present invention, the first material has a polyester film layer in at least a portion thereof. In this package of the air filter part, the first material contained in the packaging material has a polyester film layer capable of shielding permeation of organic substances. As a result, organic substances in the outside air scarcely permeates the first material to enter the inside the first material. Therefore, adhesion of organic substances to the air filter part in the packaged state is suppressed in this embodiment. The polyester film layer is preferably a film layer comprising PET.
According to a fourteenth aspect of the present invention, the package of the air filter part comprises the air filter part having in at least a portion thereof, a filter medium capable of cleaning air, and the packaging material arranged so as to shield the air filter part from outside air. The packaging material for the package of the air filter part has a first material with a polyester film layer in at least a portion thereof. The polyester film layer has a thickness of 1 xcexcm or more. As mentioned before, it has been considered that the air filter part, particularly the air filter part using the PTFE porous film having a high PF value, can maintain a clean state as when produced in a factory by being shielded from outside air by the packaging material until use. However, it has become apparent by the studies of the applicant of the present invention that those organic substances generated from outside air and the cardboard of the packaging material, permeate a PE bag and are absorbed into the filter medium. Moreover, those organic substances may be possibly generated from the PE bag itself.
Therefore, in this package of the air filter part, a polyester film layer as the first material having a thickness of 1 xcexcm is used. Thus, the polyester film layer suppresses oxygen permeability to a value lower than the predetermined value. Due to this, gaseous substances are suppressed from permeating the first material. Therefore, adhesion of organic substances to the air filter part in the packaged state is suppressed in this embodiment.
According to a fifteenth aspect of the present invention, in the package of the air filter part of the fourteenth or fifteenth aspect of the present invention, the filter medium comprises a filter layer at least partially constructed of a PTFE porous film and an air-permeable support material laminated on at least one side of the filter layer.
According to a sixteenth aspect of the present invention, in the package of the air filter part of the fourteenth or fifteenth aspect of the present invention, the filter medium has a PF value of 20 or more. The PF value is calculated by the following equation:
PF=[xe2x88x92log(penetration(%)/100)/(pressure loss(pa)/9.8]xc3x97100 in which penetration(%)=100xe2x88x92collection efficiency(%).
The pressure loss in this equation is determined by passing air through the filter medium at a flow velocity of 53 mm/sec and measuring the pressure differential between the air pressure on both sides of the filter. The collection efficiency in this equation is determined by measuring the amount of DOP having a particle size in the range of 0.10 xcexcm to 0.12 xcexcm that passes through the filter medium.
According to a seventeenth aspect of the present invention, the package of the air filter part of the sixteenth aspect of the present invention, the filter medium has PF value exceeding 22. According to an eighteenth aspect of the present invention, in the package of the air filter part of any one of the fourteenth to seventeenth aspects of the present invention, the polyester film layer has a thickness of 9 xcexcm or more. In the package of the air filter part, due to that the first material has a polyester film having a thickness of 9 xcexcm or more, oxygen permeability is further decreased. As a result, it is possible to further effectively suppress gaseous substances in outside air from permeating the first material. Further, since the polyester film layer has a thickness of a certain value or more, the first material can easily be produced. The polyester film has a thickness of preferably between 9 xcexcm and 50 xcexcm, more preferably between 9 xcexcm and 20 xcexcm. Furthermore, the polyester film layer is preferably a film layer comprising PET.
According to a nineteenth aspect of the present invention, in the package of the air filter part of any one of the eighth and thirteenth to eighteenth aspects of the present invention, the polyester film is arranged at the innermost side of the first material. In this package of the air filter part, since the polyester film is arranged at the position closest to the air filter part, the organic substances do not substantially permeate the polyester film layer even in the case, for example, that the other layer of the first material may generate organic substances. Therefore, it is possible to further sufficiently suppress adhesion of organic substances to the air filter part.
According to a twentieth aspect of the present invention, in the package of the air filter part of the nineteenth aspect of the present invention, the first material further has a PE film layer. In this package of the air filter part, the air filter part is packaged with the first material having a PE film layer which may generate organic substances. However, since the first material has polyester film layer as an innermost layer, it is possible to suppress that the organic substances completely permeate the first material.
According to a twenty-first aspect of the present invention, in the package of the air filter part of any one of the eighth to twentieth aspects of the present invention, the packaging material further has a second material arranged outside the first material. In this package of the air filter part, the air filter part is packaged with the first material, and is further packaged with the second material from the outside of the first material. In this embodiment, the first material has a polyester film layer capable of shielding permeation of organic substances. As a result, even in the case that the second material may generate organic substances, the organic substances generated from the second material scarcely permeate the first material. Therefore, even in this packaging embodiment, it is possible to suppress adhesion of organic substances to the air filter part.
According to a twenty-second aspect of the present invention, in the package of the air filter part of the twenty-first aspect of the present invention, the second material is cardboard. In this package of the air filter part, the air filter part is packaged with the first material, and is further packaged with the cardboard from the outside of the first material. In this embodiment, the first material has a polyester film layer capable of shielding permeation of organic substances. As a result, even in the case that organic substances such as DBP or DOP generate from the cardboard, the organic substances generated from the second material scarcely permeate the first material. Therefore, even in this packaging mode, it is possible to suppress adhesion of organic substances to the air filter part.
The method of packaging the air filter part according to a twenty-third aspect of the present invention comprises a first step, a second step and a third step. The first step produces the air filter part having a filter medium capable of cleaning air in at least a portion thereof. The second step is that the air filter part is packaged with the first material having a polyester film layer in at least a portion thereof such that the air filter part is shielded from outside air. The third step is that the air filter part packaged with the first material is further packaged with the second material so as to be further shielded from outside air. As mentioned above, it has been considered that the air filter part can maintain a clean state as when produced in a factory by being shielded from outside air by the packaging material until use. However, it has become apparent by the studies of the applicant of the present invention that those organic substances generated from the cardboard of the packaging material may permeate PE bag, and thus, are adhered to the filter medium. Moreover, those organic substances may also be possibly generated from the PE bag itself.
Therefore, in the method of packaging the air filter part, the first material capable of shielding permeation of the organic substances is arranged between the air filter part and the second material. Due to this, even in the case that the organic substances are generated from the second material, adhesion of the organic substances to the air filter part is suppressed. The polyester film layer is preferably a film layer comprising PET.
According to a twenty-fourth aspect of the present invention, in the method of packaging the air filter part of the twenty-third aspect of the present invention, the air filter part has a filter medium comprising a filter layer at least partially constructed of PTFE, and an air-permeable support material laminated on at least one side of the filter layer.
According to a twenty-fifth aspect of the present invention, in the method of packaging the air filter part of the twenty-third or twenty-fourth aspect of the present invention, the filter medium has a PF value of 20 or more. The PF value is calculated by the following equation:
PF=[xe2x88x92log(penetration(%)/100)/(pressure loss(pa)/9.8]xc3x97100 in which penetration(%)=100xe2x88x92collection efficiency(%).
The pressure loss in this equation is determined by passing air through the filter medium at a flow velocity of 53 mm/sec and measuring the pressure differential between the air pressure on both sides of the filter. The collection efficiency in this equation is determined by measuring the amount of DOP having a particle size in the range of 0.10 xcexcm to 0.12 xcexcm that passes through the filter medium.
According to a twenty-sixth aspect of the present invention, in the method of packaging the air filter part of the twenty-fifth aspect of the present invention, the filter medium has a PF value exceeding 22.
According to a twenty-seventh aspect of the present invention, in the method of packaging the air filter part of any one of the twenty-third to twenty-sixth aspects of the present invention, the polyester film layer is arranged at the innermost side of the first material. In this method, since the polyester film layer is arranged at the position closest to the air filter part, even in the case, for example, that other layer of the first material may generate the organic substances, the organic substances scarcely permeate the polyester film layer. Therefore, it is possible to further sufficiently suppress adhesion of the organic substances to the air filter part.
According to a twenty-eighth aspect of the present invention, in the method of packaging the air filter part of any one of the twenty-third to twenty-seventh aspects of the present invention, the second material is cardboard. In this method, the air filter part packaged with the first material is further packaged with the second material from the outside of the first material. In this embodiment, the first material has a polyester film layer capable of shielding permeation of the organic substances. As a result, even in the case that the organic substances such as DBP or DOP are generated from the cardboard, the organic substances generated from the second material scarcely permeate the first material. Therefore, even in this packaging mode, it is possible to suppress adhesion of the organic substances to the air filter part. The polyester film layer is preferably a film layer comprising PET.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.